Process of making friction material



Nov. l1, 1941.

BES/N slalom/e@ -W. NAN FELDT PROCESS OF MAKING FRICTION MATERIAL original Filed July 2, 1936 WML/AM /VAA/FEL DT ATTORNEYS Patented Nov. 11, 1941 PROCESS OF MAKING FRICTION MATERIAL William Nanfeldt, Clifton, N. J., assgnor to World Bestos Corp., Paterson, N. J., a corporation of New Jersey Original application July 2, 1936, Serial No. 88,613. Divided and this application February 21, 1939, Serial No. 257,664`

8 Claims.

'I'his invention relates to the manufacture of friction material. More particularly, the invention pertains to a molded friction material and a process for making the same having utility in connection with clutch facings, brake blocks, brake linings and miscellaneous other friction elements for mechanism.

lAmong the objects of the present invention is to provide an improved process for making brake lining which will enable the manufacture of lining to be completed within a short time interval after themixing of the component ingredients. Another object is to provide a process which will reduce to a minimum the formation of surface fissures or cracks on the lining slabs during the intermediate steps of the process. Still another object is to provide a process for making brake lining which is susceptible to efcient control of the various reactions occurring during the treatment of the composite material, such as the degree of hardness, the resiliency of the product, the extent of hardening of the resinous ingredients, the degree of combination of the sulphur and linseed oil, and other reactions.

An object of the invention also is to provide a product which has a hardness not exceeding 3`Mohs. l A further object is to provide a friction product which has uniformity of frictional coefficient for normal ranges of temperature as well as temperatures approximating 900 F. An object also is to provide a friction material having properties through which noise of operation is practically eliminated. Further objects of the invention relate to the high normal and shear resistance of the nished lining, to the employment of certain materials which will not materially modify under the influence of heat within the usual range of use, to the provision of materials in a brake lining having flat particle formation susceptible to breakage With sharp, jagged or conchoidal fracture, and other features such as will appear from consideration of the following description of my invention and the accompanying drawing.

In my co-pending application Serial No. 29,763, filed July 3, 1935, issued as Patent No. 2,155,020, I describe a molded friction lining of high utility, in the process of manufacture of which use is made of at least three compositions denoted as compositions A, B and C, composition B forming the framework of the brake lining and including materials giving a more or less rigid structure to the same; composition A being formed of materials which develop an eicient frictional coeffcient and which are dispersed through the cellular construction of the B composition in spaced masses; and composition C being formed of Inaterials suitable for forming a backing for the primary friction compositions A and B.

In the present application, which is a division of my co-pending application issued as Patent No. 2,175,480, I will describe a composition and the process for making the same, which in some respects is an improvement over the process and product described in my copending application Serial No. 29,763 and issued as Patent No. 2,155,020, above notedgiving a friction lining in which the frictional coeflicient diminishes by less 'than 35% in the vicinity of 900 F. In the composition of this application, similarly I employ three compositions A, B and C, the function of each of these compositions being similar in function to that of the allied compositions in the c0- pending application referred to, the composition A forming the primary friction material; composition B constituting the holding and framework material; and .composition C forming the backing for the friction lining or material.

The composition which I denote as composition A, together with a permissible range of percentages and an example of preferred percentages, is as follows:

Materials Ranges Example Percent Percent 2% blown sulphurized linseed oil 5 to 18 14. 28 Liquid cresol resin 2 to 18 8. 79 Sulphur 1 to 3 2. 20 XX asbestos fibre 45 to 65 60.45 Albany sllp clay- 5 to l5 9. 88 Iron oxide l to 4 2. 20 mesh powdered mica 1 to 4 2. 20

The 2% blown sulphurized linseed oil is a sulphur-linseed oil mixture made by mixing boiled, bodied or blown linseed oil with 2% of its Weight of sulphur to a temperature of about' 350 F. for a time period sufficient to cause the oil to take up and absorb the sulphur. By so treating the linseed oil, oxidation, together with 'the undesirable hardness resulting therefrom, is prevented.

The resin element of the composition is in the form of liquid cresol resin. I have found this form of resin to be desirable in the friction `A composition since it reduces to some extent the resiliency of the composition and assists in the controlling of the reactionbetween the sulphur and thesulphurized linseed oil in the subsequent bakingk operation. This latter characteristic of the resin comes from the fact .that the resin does not combine withsulphurized linseed oil, but on the contrary, tends to form an emulsion therewith, thus slowing'down the reaction between the oil and sulphur. When heated over a suiiicientV length of 4time the cresol Aresin passes over into the'infusible state Where it has a Mohs scale hardness ofslightly less than 3.

The` sulphur employed is the pure flowers of sulphur finely ground so as to readily combine with the linseed oil in the baking operation. The

n ness ranging from 3 to 3%.; Mohs.

a resilient element in the friction substance, the y compound having properties somewhat similar to.

I prefer toy use Albany 'slip clay,

that of rubber. i y i 1 but any other clay havingparticles with similar addition to these two ysubstances employ, as appears 'fromthe above list, materials other than that used in the A composition.

HHexamethylenetetramine is used in small 'amounts to act as a catalyzer or hardener, this j substance tending to hasten the polymerization physical characteristics such as Ja plate-like .and

perforated formation and a hardness according to the Mohs scale of approximately 2 may be employed. The function ofthe slip clay is to prol vide a ller which assists in controlling the resiliency and density of the A composition. The clay also has a lubricating nature and when mixed with sulphurized linseed oil it assists materially inthe mixing operation of the A composition in the dough mixer. .v i A I employ powdered mica which will pass through a 150`to the inch mesh, and'the'type knownras Vamber mica or its equivalent is preferred. The purpose' of the mica is to provide a compositionl material which'is of plate-like particles and therefore resistant ytov pressure. The mica is formed in laminated sheets and is more or less brittle and'when subjected Yto shearing pressure tends Ltodelaminate, causing the frictional surface of the lining to shift and thereby assisting in the stabilizationof the surface friction and tending to prevent glazing or polishingof the same.

, Iron oxide is used inthe A composition in the form of a fine powder having 4a low frictional value and a Mohs scale hardness 1 of around 2.1/2 The characteristic action of the iron oxide particles 'is to assist in the control rof the frictionaly value of the finished lining through the tendency of ythe particles to take on valpolishi under pressure. Y

kThe asbestos libre is known in the trade as fdouble X (XX) and consists of mine run asbestos having short lfibres which has been treated in a rotary disintegrator to shred and separate the bundles of fibres. After such treatment it. is found that the hardness is reduced to lslightly less thafn 3 Mohs over the normal asbestos hard- In this treatment also rock clust and other foreign matter Vis removed.

Thecomposition WhichiI-denote -as composition B," together With Va permissible range of lpercentages and an example of preferred percentages. is as follows: 1

- Materials Ranges Example Percent Percent Powdered cresol resin 15 to 30 v27; 21 Hexamethylenetetramine 1 to 3 1.36

Carbon black... 0. 5 Ato 3V 1. 36

Blood albumen 1 to 6 5. 44

Shingle asbestos bre 38 to 50 44. 90

Fusedfand pulverized lit g 1 to`10' 5. 44

Scrap of nal mixture l to 15 y 13.61

As .will be seen from this list, cresol resin is employed also in the B groups vof m-aterials but in.

powdered instead of liquid form. Asbestos is alsof,

employed but of a type known as shingle asbestos.` This asbestos Adiffers over thedouble X asbestos fibre in that it is obtained by treating longvbred asbestos in a disintegrator, a 'shaker and blowen;v and then subsequently re-run through thedis-l, integrator to further breakup the fibres so thatl the average fibre length of there-ground fibre is approximatelythe'same asl the double X mineruniibre,v that is, approximately %j or less.' Inl of the cresol resin with heat. Carbon black has been found useful as a part of the brake lining Ystructure asa controlling factor in the surface friction of the material. The carbon black is in `the'form of very vsmall particles which spread .The advantages of using metallic lead in k@a frictional surface ysuch as a brake lining have beenknown for some time. However, the melting point of lead is around 621 F. and hence at the high temper-atures now employed in heavy duty lining, amounting to points in excessk of 800 F., the lead is melted and its function asv a friction element under th-ese high temperatures destroyed. I have found that by using litharge, which has a much higher melting point, I can make the lead arising from a decomposition of the litharge effective at these high brake lining temperatures. To accomplish this breakdown of the litharge I employ blood albumen, which has the property of combining with the oxygen `of the litharge when mixed with ground and pulverized litharge and heated -to a temperature approaching 800 F., at which 'temperature the albumen tends to decompose and combine withA the oxygen and liberate free metallic lead. The lead liberated atgthese high temper--v atures has a stabilizing value ,on the friction since, with other properties,it s hifts on the friction face, preventing a hard, smooth and car-kr bonized surface .fromA forming.

l. The albumen, in addition to fcombiningwith the litharge, tend to prevent the lining from u beingv `noisy when used in contact with brake drums. This isv probably due to the fact that it does not melt to a fluid with Vheat but becomes slightly plastic and as the temperature rises is around 2. A type or blood albumen which I' found to be highly satisfactory for this use has been analyzed to indicate the following composition:

Components L APercmt Water A Total 'solid matter 0.083 Phosp. cid as nuclcin 0.0027 Sodium oxide 0. 364 Potassium oxld f 0. 041 Iron oxide. 0.054 Calcium oxide 0. 008 Magnesium-oxide 0. 0036 Chlorine O. 308 Phosphoric acid 0.040 Inorganic P205 `0. 017

' The lithargeused is madeby heating lordinary litharge until itk melts to ajjfluid, and'after it has cooled andfsolidiedgrinding and pulver- Whole blond izing the same so that it will pass through la 100 Vto the inch mesh screen. 'Ihese litharge particles are similar to flat plates in structure vwith jagged edges which make them effective Materials Ranges Example Percent Percent Powdered cresol resin 18 to 28 24. Carbon black 25 to 3 1.00 Shingle asbestos fibrem.. 50 to 70 69.00 Scrap of final mixture 1 to 10 6.00

It is noted that the various compositions are described each as a unit, the component materials forming 100%. In relation to the final composition, as for example, in the brake lining, the percentage of the group materials in a typical example may `be varied Within limits, such as 10% to 40% of the A group, 20% to 50% of the B group, and 5% to 30% of the C group. A typical percentage relationship is: group A-29.2%, group B-50.8%, and group C-20.0%. Further, as regards the individual materials entering into the completed composition or brake lining, the percentage ranges and a typical example follows:

Materials Ranges Example Percent Percent 2% blown sulphurized linseed oil 2 to 8 4.17 Liquid cresol resin. 2 to 8 2.57 Sulphur 0.25 to 1 .64 XX asbestos bre to 25 17. 66 Albany slip clay 2 to 5 2. 89 Iron oxide 0.25 to l 64 150 mesh powdered amber mica. 0.25 to l 64 Powdered cresol resin to 20 18. 62 Hexamethylenetetramine. 0.25 to 1 .70 Carbon black 0.25 to 1 90 Graphite 0.25 to 1 35 Blood albumen 1 to 4 2. 76 Shingle asbestos fibre to 40 36. 60 Fused and pulverized litharge.. l to 5 2. 76 Scrap of final mixture 1 to 10 8. 10

In carrying out the process of making friction material from the substances mentioned? land in accordance with the assemblage of these substances in groups A, B and C, the materials of each group are independently assembled andt subsequently combined in |a unified mass for treatment. In the case of the group A materials, the powdered mica, the iron oxide and the slip clay are mixed in a ball mill for about fifteen minutes or until a uniform mix of these constituents is obtained. A mill of this type is made by the Paul Abbe Company. Double X (XX) asbestos fibre, as previously described, is added to the mix from the ball mill and the assembled materials treated in a tumbling barrel for about Oife-half hour or until the non-fibrous filling material has been dispersed and distributed throughout the asbestos fibres. The contents of the tumbling barrel is then. placed in a dough mixer such as that manufactured by Warner & Tfleid'erer. To the dough mixer is added also the sulpherized linseed oil, liquid cresol resin and black, blood albumen, graphite and the fused and sulphur which previously has been stirred to- 'gether cold in a pony mixer until the sulphur is finely distributed throughout the oil and resin. The dough mixer is operated for about one and vone-quarter hours or until a uniform mix of vtor such as that built by Christie & Norris Company, including a rotating drum with a corrugated lining and opposed vanes. By the action of this machine the lumps and clusters of fibres and other material which may have been formed in the dough mixer are broken up into small ball-like and usually semi-dry particles. The material is then placed in shallow pans and inserted in an oven where at a temperature of around 225 F. it is retained for a period of about three and `one-half hours. This completes the preparation of the A composition and. it is now in condition to be added to the B composition.

In preparing the B composition the nonfibrous material including the powdered cresol resin, the hexamethylenetetramine, carbon pulverized litlrarge are mixed together in the ball mill until uniformity of mix is obtained. The shingle asbestos fibre, as previously describ'ed, which has been properly cleaned, freed from .rock dust, opened and fluffed, is then added to the non-fibrous material in a tumbling barrel which is tumbled and mixed for a period of approximately one-half hour or until the nonfibrous iilling material has been thoroughly dispersed through th'e asbestos fibres. At this point, that is, after the mixing of the nbrous and nonfibrous stock in the tumbling barrel, the A composition mix is added together with scrap of the final product and the mixture of the A and B compositions are tumbled for about a half hour, after which they are removed from the barrel land passed through the disintegrator. The action of the disintegrator is to break up any large lumps or clusters of bres which have been formed in the materials and obtain a more thorough mix of the two groups of substances. The product as obtained from the disintegrator and consisting of a mixture of groups A )and B materials is the final mixture and includes all the materials that enter into the friction face of the completed lining. The accompanying drawing indicates in flow sheet form the process of making the nal friction material as above described.

There remains to describe the preparation of the C composition mixture. A ball mill is utilized as the first operation in the treatment of the C composition materials, the non-fibrous substances, carbon black and the powdered cresol resin being introduced into this mill and thoroughly mixed. The resultant mixture, together with the shingle asbestos fibre and scrap of nal mixture, is then introduced into a tumbling barrel where these materials are tumbled until a uniform mix is obtained and the non-brous materials distributed throughout the fibrous stock. 'Ihe mixture is then passed through a disintegrator to break up clusters of bres and balls of the substance, thus obtaining the final mix.

In describing the molding steps of the process the description will be limited to the formation of a brake lining. In carrying out this step oi the process a preliminary flat sheet of the material is rst obtained. Any suitable means for plate.

F. for about four minutes. 'tion under heat and pressure the libres are comtimes the finished thickness of the C layer. Upon this C composition layer a predetermined amount of the mixed A and B compositions is evenly distributed to such a depth that the thickness of the A-B-C layer is approximately times that of the molded segment. The plunger part .of the mold is then put in place and the material pressed cold in a suitable press at about 125 pounds per square inch to a thickness `approximately ve times greater than the required thickness of the -iinished segments.

This preliminary sheet or slab of friction material vdoes not have suflicient strength for handling but must be handled on suitable trays. In .removing the compressed preliminary slab from thepreliminary mold, the plunger and the Vside frame of the mold is lifted upward to free the top and bottom of the slab. A sheet of Cellophane about 0.001 inch thick is laid over the top of the preliminary sheet or slab and extended over the Aedges of the same about 1/2 or at least equal to twice the finished thickness of the slab. Upon this sheet of C'ellophane is laid a flat sheetmetal plate which has the approximate length and width of the slab. With the sheet of Cellophane and the metal plate in place on top of the slab and the slab lying upon the false bottom of the mold, the whole unit is reversed so that the slab is nowlying upon the sheet of Cellophane and the isheet-metal plate. The bottom part of the mold may then be removed and another sheet of cellophane placed on the slab, this sheet, however, being of the same length and width as the slab. lUpon this second sheet of Cellophane isv laid another sheet-metal plate which has the same lengthuand width as the Abottom sheet-metal The preliminary sheet or slab is now a vunit which is ready for the heat treatment.

In `carrying out the heat treating step of the Aprocess the preliminary slab, including the supporting metal and Cellophane sheets, is placed in the bottom of a heated single cavity plunger type mold which is slightly larger than the slab and ls y'here subjected to pressure of about 800 pounds per square inch at a temperature of around 290 During this operapacted and the powdered cresol resin melts and flows around the bres and non-fibrous material and starts to react and polymerize. The hexamethylenetetramine in the composition also melts and starts to combine with the cresol resin. 'This this operation that the powdered cresol resin melt to Va fluid before starting to polymerize and that the compressed composition slab is removed from the mold at the point where ythe cresol resin is melted to a fluid and just starts to polymerize. The compressed sheet and the supporting metal plates are removed from the pressure of 800 pounds, however, is not suc'ient f to produce the maximum density desired and reduces the thickness of the material to 'a value at least 1.2 times greater than the thickness of the finished friction material. If maximum density were imparted at this Ystep of the process it would beimpossible to 'curve the sheet 'without cracking; even though the ybond were still fluid or plastic'. Another reason for not imparting maximum density 'to the heated slab is that blistering is apt to occur while removing the compressed sheet mold while hot by admitting air under pressure to the bottom side of the bottom plate, this forcing the slab upwardly where it can be secured and removed. The sheet-metal plates are at once removed froml the slab and the composition sheetk is bent over a suitable mandrel having a desired curvature. sheet is then quickly placed in a curved sheetmetal pan and the pan placed in a cold curved cavity mold where the sheet'is allowed to cool while under a pressure of about pounds per square inch. After this curved sheet is cold the preliminary treatment will have been completed and the sheet may be stored in this form or* `materia-l to a uniform arc in the bending operation and preventing cracking of the material.

The final treatment of the semi-cured slab` consists in the complete cure of the material which is -accomplished .by placing the curved composition sheet in a curved sheet-metal pan and placing lthe pan in Ya curved cavity mold where, under a pressure of around 1500 pounds per square `inch at a temperature of approximately 300 F. for a time period of about one hour, the maximum Idensity is imparted to the sheet and the cresol resin passes over into the infusible state. In this pressure operation the Cellophane which still adheres to the curved sheet prevents sticking of the sheet to the metal pans. After removal from the curved mold the sheets are cooled and may be stored in stock for further processing in this slab form.

Proceeding with the operation, the curved sheet is cut into segments of the required widths by any suitable means and then ground on all sides -to the required dimensions. The individual ground segments are lthen yplaced on trays or any suitable conveyor in an oven Where they are baked for approximately two hours while heated ata temperature yaround 225 F. In this final baking operation vthe .trapped .gases are removed,

the resinous bond .in the B and C compositions is .completely transformed to its infusible state and the sulphurized linseed oil in the A composition takes .on its final resilient set. After the baking is completed the segments are removed from the oven .and cooled, this completing the manufacture of the brake lining.

Instead vof cuttingl the curved cured sheets 'into segments they may be ground on all sides and baked as in the case of the individual segments and furnished tothe jobbing trade where dealers may cut various sizes of segments from the sheet or vslab asdesired.

The -nal friction lining as made by the above processl consists of areas of rigid material derived from the B composition and intermediate areas of resilient material derived from Vthe A composition, the B composition material serving as a `framework `for supporting the A composition This curved composition material. The C composition in the final product has a thickness of approximately 11e but may vary from one-fth to one-twelfth of the thickness of the finished lining, depending upon the lining thickness. For example, in a 13e" 1ining the C composition is approximately one-fifth of the thickness.

Of the various materials employed in the friction lining as above described, as previously mentioned, each has its particular function in cooperating to make the brake lining effective. In general the different materials have a hardness of 3 Mohs or less, so that the composite hardness of the lining is 3 Mohs or less, and consequently it is impossible to scratch the metal surface of the cooperating brake drum which is made of cast iron or soft seel. The various particles for the most part have a nat, plate-like formation highly resistant to normal pressure b-ut at the same time breaking down under shear pressure with jagged edges tending to resist side movement and thus intensify the frictional effect. The use of materials such as mica and carbon black serve to prevent glazing and unstable friction properties; the use of slip clay provides density factors as Well as assists in the mixing process; the linseed oil in conjunction with the sulphur provides the resilient yielding factor to the brake lining surface; the litharge supplies an effective frictional element for high temperatures; the asbestos binds the various substances together throughout the temperature range of use; land the resin forms the base of a rigid framework or holding means for the primary friction substances. With these materials assembled according to my process I am able to manufacture a brake lining which maintains practical uniformity of the coeicient of friction up to temperatures around 400 F. and at 900 F. has diminished from this uniform value by less than 35%.

While I have specified certain materials as entering into this composition, it is of course apparent that equivalent substances may be substituted. For example, for the cresol resin may be substituted cresol formaldehyde resin, phenol furfural resin-s, other furfural resins or certain types of synthetic resins which will become infusib-le with heat and not exceed a hardness of 3 Mohs. Instead of blown, bodied or boiled linseed oil certain other vegetable oils such as China-wood oil, either alone or in combination,

may be used, or a limited amount of rubber, to supply the resilient factor. Instead of carbon black other carbon sources such as coal tar coke might be employed. However, the particular elements forming the composition hereinabove described have been found to be superior in the relationships named.

I claim as my invention:

1. A process of making brake lining material which comprises heating linseed oil with about 2% by weight of sulphur, mixing the sulphurized linseed oil with cresol resin and additional sulphur, combining the'resultant mixture with a base composition of mica, iron oxide and clay, oven-heating the resultant mix, adding the mix vto another composition containing mixed powdered cresol resin, hexamethylenetetramine, carbon, albumen, graphite and litharge to form the final brake lining material.

2. A step in the process of making brake lining material containing asbestos fibre, litharge, albumen, liquid cresol resin, sulphur, and linseed oil which comprises mixing linseed oil and about 2% by weight of sulphur at a temperature of about 350 F. and then mixing the sulphurized linseed oil with the liquid cresol resin prior to addition to-the other materials.

3. A process of making brake lining material which comprises heating linseed oil with about 2% by weight of sulphur, mixing the sulphurized linseed oil with cresol resin and additional sulphur, combining the resultant mixture with a base composition of mica, iron oxide, asbestos and clay, oven-heating the resultant mix to form a first composition, and adding the first composition to a second composition containing cresol resin, hexamethylenetetramine, carbon, albumen, graphite, asbestos and litharge to form the nal brake lining material.

4. A process of making brake lining material which comprises mixing linseed oil with about 2% by weight of sulphur to form a sulphurized linseed oil, combining the resultant mixture with additional sulphur and a base composition of mica, iron oxide, asbestos and clay, oven-heating the resultant mix, and adding the mix to another composition containing litharge and friction materials to form the final brake lining.

5. A process of making brake lining material which comprises heating linseed oil with about 2% by weight of sulphur, mixing the sulphurized linseed oil with cresol resin and additional sulphur, combining the resultant mixture'with a base composition including asbestos, oven-heating the resultant mix, and adding the mix to another composition containing litharge and additional friction materials to form the final brake lining material.

6. A process of making brake lining material which comprises heating linseed oil with about 2%I by weight of sulphur to a temperature of about 350 F. for a time period sufficient to cause the oil to take up and absorb the sulphur, mixing the sulphurized linseed oil with liquid cresol resin and sulphur, combining the resultant mixture with a base composition of mica, iron oxide, clay and asbestos, breaking up the resultant mix into small particles, oven-heating the material, combining the oven-heated material with a mixture containing cresol resin, hexamethylenetetramine, carbon, albumen, graphite and litharge previously mixed with asbestos, and mixing and disintegrating the combined friction elements to form the final brake lining material.

'7. A step inthe process of making brake lining material containing asbestos fibre, litharge, albumen, liquid cresol resin, sulphur and linseed oil which comprises mixing linseed oil with about 2% by weight of sulphur at a temperature of around 350 F., mixing liquid cresol resin and sulphur at room temperature, and then combining and mixing the sulphurized oil and mixed resin and sulphur until the sulphur is finally distributed throughout the oil and resin.

8. A process of making brake lining material litharge, combining the last named ingredients with asbestos to form a second composition, and

finally intimately combining the two compositions to form the final brake lining material.

WILLIAM NANFELDT. 

